Method of and means for reducing electrical disturbances



Nov. 20, 1934. D. G. McCAA 1,981,457

METHOD OF AND MEANS FOR REDUCING ELECTRICAL DISTURBANCES Filed Oct. 29, 1950 Patented Nov. 20, 1934 UNITED STATES METHOD or AND MEANS FOR Ii DUCING ELECTRICAL DISTURBAN'CES David G. McCaa, Philadelphia, Pa. Application October 29, 1930, Serial N0."492,053. 2 Claims. (CL 250- 20) The present invention relates to improvements in means for reducing and limiting interfering pulsations in electrical circuits through which electrical energy is being transmitted in useful form and especially to apparatus and methods adapted to reduce theinfluence of atmospheric or any other electrical disturbances in signal-receiving device originating externally of the device and is a specific application of the invention disclosed and claimed generically in my co-pending application, Serial No. 320,849, filed Nov. 21, 1928, which in turn, is a division of my application, Serial No. 74,087, filed Dec. 8, 1925; The present invention is in the nature of a specific embodiment or modification of the generic invention disclosed in my co-pending applications, Serial No. 492,052 filed Oct. 29, 1930, and Serial No. 492,054, filed Oct. 29, 1930.

As is well known, when electrical disturbances are in evidence during radio reception, they take the form of audible noises which often completely submerge all other reproduced sounds. The origin of such disturbances cannot be readily controlled nor their arrival at the antenna prevented. Hence the place where their effects may be decreased is confined to the vicinity of the receiving system itself. To reduce or substantially eliminate the effects or" the oscillations, by which such disturbances are produced, requires that such oscillations be so far as possible nullified and one method of accomplishing this purpose is to reduce the ratio of the energy due to disturbing oscillations to the energy due to the desired or signal oscillations. It is, therefore, the object of the present invention to provide a method and apparatus so designed that the effects of electrical disturbances can be controlled and largely reduced Without substantially affecting the quality of reception of desired signals, thus permitting the reception of signals with great deal more clarity and substantially as great intensity as when no disturbances are present. I

Another object is to provide an improved method and device for differentiating in electrical circuits between impulses of electrical energy of different amplitudes, the higher amplitude waves being damped as, for example, atmospheric static or other similar electrical disturbances and the lower amplitude wave being the desiredv signal wave. 1 I

Another object of the invention is to provide a method and apparatus by which the efiects of electrical disturbances may be substantially reduced to a point where they are no longer troublesome and which can be operated in connection with an ordinary receiving system in either radio or telephone line communication. 3 The apparatus in this respect, including appliances, may be dis: posed either between thereceiving system and the input thereto or connected into the circuit of the receiving system between the output of the sys tem and the soundreproducing device, or in any otherconvenient position in the receiving system. Other objects and advantages of the invention will appear more fully hereinafter from the followingdetailed description taken together with the accompanying drawing, in which: I The single figure is -a schematic wiring diagram illustrating anarrangementfor carrying out my invention. Referring to the drawing, anantenna circuit 1 isshown having a pair of windings 2 and 3 therein and being connected to earth or ground in the customarymannen. windings 2 and 3 act as input coils for independent circuits .respectively.' Secondarywinding 4 is inductively associated with winding 2, while a pair of secondary windings 8 and-9 connected inseries are inductively associated with winding 3. While my device is shown as appliedto the radio frequency portion of the receiving system, it may as well be applied to the audio frequency portion, in which case, windings 2 and 4 wouldbe wound on the sameiron core and windings3, 8 and-9 would likewise be Wound on a common iron core. The upper terminal-of winding 4 is connected to one side of a variable resistor 5, the other side of which is connected-to aterminal of winding 6. The. other terminals 'of windings 4 and 6 are connected together. A pair of thermionic devices '10 and ll, which, in the present instance, are illustrated asordinary three electrode vacuum tubes having the usual grid, cathode and anode, are connected in push-pull relation with respect to each other. The upper terminal of winding 8 is connected to the grid of tube 10, while the lower terminal of winding 9 is connected to the grid of tube 11. The other terminals of windings 8 and 9 are connected to each other and to a variable contact of potentiometer 13. A -source of-uni-directional potential 12 is connected to potentiometer 13 as shown. A common lead'connects the cathodes of the tubes to the potentiometer and battery. It will be noted that the polarity of source 12 is such as to provide a common negative grid biasing means for the two tubes, the potentiometer being adapted to cause-varying biasing potentials to be applied to thegrids of. the tubes.

The anodes of tubes 10 and 11 are connected respectively to the upper and lower extremities .of windings 15 and 16. A common lead connects the other terminals of these windings to the posi tive terminal of the anode potential supply source 14, the negative terminal of the source being connected to the cathodes of the tubes. A secondary winding 7 is inductively associated with winding 6, while secondarywindings 17 and 18 are inductively associated with windings 15 and 16, respectively. audio frequency portion of a receiving system, the windings would, of course, be wound on common cores, as stated before. One terminal of the winding 7 is connected'to an output terminal 20, while the other terminal of winding 7 is connected to winding 1'7. windings 17 and 18 are connected in series, the otherterminal of winding 18 being connected to'output' terminal 19. It will be noted that winding 7 is so con nected with windings 17 and 18 as to act in opposition thereto.

The biasing potential applied to the grids of tubes 10 and 11 may, as stated before, be adjusted by means of potentiometer 13 within limits of source 12. In the present instance, potentiometer 13 is first adjusted to so bias the grids that normally with no incoming oscillations no plate current flows in the output circuits of the tubes. That is, the tubes are adjusted tooperate on their characteristic curves at zero plate current. Potentiometer 13is then further adjusted to cause an additional bias to be applied to the grids of the tubes. This additional bias is of such a value as to equal the peak potential values of low amplitude or signal oscillations.

Let us assume that the antenna circuit is being excited by incoming oscillations. Such oscillations, regardless of their polarity or amplitude, set up or induce corresponding oscillations in winding 4. Currents, varying in amplitude according to the incoming oscillations, will flow in winding 6 and corresponding currents will be induced winding 7 and appear in the output circuit of the device. The amplitude of the currents flowing in the circuit of windings 4 and 6 vmay,of course, be varied by means of the variable" resistor 5. This resistor, of course, has a straight --line impedance characteristic and is nondiscriminating so far as the amplitudes of the incoming oscillations are concerned.

Assume that an incoming'oscillation is such as to induce a voltage across winding 3 so that the upper'terminal of the winding is negatively poled, the lower terminal being positively poled. A'corresponding voltage will then be set up across coils 8 and 9, the upper extremity of winding 8 becoming negatively poled and the lower extremity of winding 9 becoming positively poled.

V The voltage across winding 8 will then act to assist the biasing potential applied to tube 10 and-will cause the grid of tube 10 to become even more negative, thereby blocking the tube. At

. the same time, however, thevoltage across winding 9 acts in opposition tothe biasing potential of tube 11-and tends to cause the grid of tube 11 to go positive, thereby making the tube conductive. If the incoming oscillation is of an amplitude higher than the peak potential of the desired or'signal oscillations, the potential across winding 9 will overcome the biasing potential of tube 11 and cause it to become conductive. A plate'current, whose amplitude is proportional to the applied oscillations will then appear in the output circuit of tube 11 and will flow through winding-16 in thedirection indicated by the ar- If the device were used in the row. This current flowing through winding 16' will induce current in winding 18 which will flow in the output circuit as indicated by the arrows. Since a voltage of similar polarity has been set up across winding 2, currents will flow in the circuit of resistor 5, as indicated by arrows and an opposing current will flow in winding 7.

On the next half cycle of the incoming oscillation, current will flow in the opposite direction in the circuit of resistor 5 regardless of the amplitude of the oscillation. At the same time, the. polarity of the potential across windings 8 and 9 is also reversed and tube 11 becomes more negatively biased while tube 10 becomes conductive for amplitudes greater than the peak potential of the desired signal oscillations. For amplitudes lower than the peak potential of the desired oscillations, tube 10 is also blocked and is non-conductive. The large or disturbing oscillations cause a flow of plate current in the output'circuit of tube 10 through winding 15 in a direction opposite to that of the previous current flow through winding 16. The current induced in the output circuit by winding 15 is, therefore, opposite in direction to that which previously flowed. However, the flow of current through winding 7 has likewise reversed and the currents in the output circuit again oppose each other. i

i It will be apparent that currents due to both signal and disturbing oscillations will flow in the circuit ofv resistor 5 during each half cycle of each incoming wave, a reversal in direction thereof taking place each half cycle. other hand, the circuit of tubes 10 and 11 is non-conductive to currents caused by low amplitude or signal oscillations by virtue of the common biasing source 12. If the incoming oscillations are of greater amplitude, however, than the peak value of the desired oscillations, the tubes alternately act during each succeeding half cycle to conduct the disturbing currents. Cor-' responding disturbing currents will, therefore, be induced in different directions in windings l7 and 18 during each half cycle of the incoming oscillations. The disturbing currents which flow through winding '1 will, therefore, oppose and neutralize the disturbing currents flowing through windings 17 and 18, while the signal current flowing through winding '7 will be unopposed and will flow to any device connected across the output terminals 19 and 20. The circuit of resistor 5, therefore, constitutes a non-. discriminating device, while the circuit of tubes 10 and 11 constitutes a device which discriminates against the low amplitude signal oscillations. I I

Suitable means such for instance as variable resistor 5 must be provided to cause the amplitude of voltage transferred by paths 2, 4, 6, '7 to substantially equal the amplitude of the voltage transferred by paths 3, 8, 10, 15, 17 and 3, 9,11, 16,18, so that a substantial nullification of voltage occurs when either tube 10, or 11 conducts. Any method of lowering or raising the voltage transferof either circuit may be used, which does not discriminate with respect to amplitude,

On the 1 ifs its

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frequency, or phase, as compared with the other iso by the prior art as reflected by the scope of the appended claims.

I claim:

1. In a device for discriminating between electrical waves of difierent amplitudes, two electrical paths operative with respect to the source of said waves, two thermionic devices, each including an anode, in one of said paths arranged to conduct alternately the half cycle portions of said waves, means biasing said devices beyond anode current cut-off an amount comparable to the peak value of waves of predetermined amplitude, and means for opposing to each other the waves passing through said paths, whereby waves of greater amplitude than said predetermined amplitude substantially cancel each other.

2. In a device for discriminating between electrical waves of different amplitudes, two electrical paths operative with respect to the source of said waves, an impedance device in one of said paths, two thermionic devices, each including an anode, in the other of said paths arranged to conduct alternately the half cycle portions of said waves, means biasing said thermionic devices beyond anode current cut-off an amount comparable to the peak value of waves of predetermined amplitude, and means for opposing to each other thewaves passing through said paths, whereby waves of greater amplitude than said predetermined amplitude substantially cancel each other.

DAVID G. McCAA. 

